Tyre pressure and grip in a corner
Tyre pressure is the one grip setting you can change in a minute with a pump. Lower pressure, within what your tyre and rim allow, gives a bigger contact patch, more wet grip in the rig tests below, and a tyre that follows rough asphalt instead of bouncing off it. In Krengo’s model the pressure effect is a few degrees of limit, not the eleven degrees that wet asphalt takes. That makes it a nice, cheap gain.
About the numbers. Pressures and wet-grip values come from the linked manufacturer and test-rig sources and are written as such. Lean angles and percentages are model values with the same assumptions as the grip scale and cornering in the rain. Krengo does not measure tyre pressure or grip; the grip colour is an estimate from lean angle and assumed values. The field itself is not released yet.
Width, pressure and the contact patch
A pneumatic tyre carries the wheel load on air pressure, so in the simplest model the contact area is the load divided by the pressure: A = F / p. For a wheel carrying 40 kg (about 392 N) that gives the areas below. The widths are paired with the pressures the tyre tester used for each size of one tyre model.2
| Width | Test pressure | Ideal contact area |
|---|---|---|
| 25 mm | 5.5 bar (80 psi) | ≈ 7.1 cm² |
| 28 mm | 5.0 bar (72 psi) | ≈ 7.8 cm² |
| 30 mm | 4.8 bar (69 psi) | ≈ 8.2 cm² |
| 32 mm | 4.5 bar (65 psi) | ≈ 8.7 cm² |
It is a textbook idealisation: the casing carries some load too, so real patches are somewhat smaller, and a rider’s weight is not 40 kg per wheel in every position. The direction is what matters. Going from 25 to 32 mm at the recommended pressures gives roughly 20 % more area, and every extra bar takes some away (at 7.5 bar the same wheel has about 5.2 cm²). Contact area alone does not set friction, because rubber is not an ideal block, so the next step is what testers measure.
What the wet-grip tests show
A test rig pressed three 28 mm road tyres onto a wet, textured ceramic plate at four pressures. Lower pressure gave more grip, and the centre of the tread reacted more than the edge.1 The edge matters most when you lean, since the bike then rides on the shoulder of the tyre. The last two columns turn the rig’s values into the raw limit tan θ = μ.
| Pressure | Centre grip | Edge grip | Raw limit, centre | Raw limit, edge |
|---|---|---|---|---|
| 3.7 bar (54 psi) | 0.78 | 0.77 | ≈ 38.0° | ≈ 37.6° |
| 5.0 bar (72 psi) | 0.74 | 0.74 | ≈ 36.5° | ≈ 36.5° |
| 6.2 bar (90 psi) | 0.71 | 0.73 | ≈ 35.4° | ≈ 36.1° |
| 7.4 bar (108 psi) | 0.69 | 0.72 | ≈ 34.6° | ≈ 35.8° |
Across the whole range the centre moved by about 3.4° of raw limit and the edge by about 1.8°. These are rig numbers on a flat plate, not road values: the grip scale assumes 0.60 for a wet road, well below the rig’s 0.69–0.78. What carries over is the size of the change, roughly 6 % of grip at the edge and 12 % at the centre between the highest and lowest pressure.
What that is worth in the model
Take the corner from the rain article: 15 m radius, 30 km/h, about 25.3° of lean, level Settled. On wet asphalt (μ 0.60) the model uses about 123 % of the assumed capacity. If the wet road responded like the rig’s edge, a 6.5 % drop in grip from lowest to highest pressure would take that to about 131 %; with the centre’s 11.5 %, to about 139 %. For comparison, speed does the same work: 30 km/h is 123 %, 29 km/h is 115 % and 27 km/h is 101 %. So the pressure effect in the edge case is worth about 1 km/h of corner speed. It is real and free, and a good line and a gentler entry still do more.
Wider tyres: more wet grip in the same test
The same tester measured one tyre model in four widths, each at its recommended pressure. Wet grip rose with width, and the tester’s conclusion is that bigger tyres provide more grip.2 The scores are the tester’s own scale, not a friction coefficient.
| Width | Average | Centre | Edge |
|---|---|---|---|
| 25 mm | 66 | 67 | 65 |
| 28 mm | 67 | 68 | 67 |
| 30 mm | 68 | 69 | 67 |
| 32 mm | 71 | 72 | 69 |
Part of that gain comes from the lower pressure the wider tyre runs, part from its shape, and the test does not separate the two. Both point the same way for a road rider who has room in the frame.
Wet against dry
The wet gap is bigger than the pressure effect. The grip scale puts the raw limit at about 42° on dry worn asphalt (μ 0.90) and 31° on wet (μ 0.60), a difference of 11°, against 2–3° from pressure in the rig. The source above tested wet grip only, so there is no matching dry table here; the grip scale does not make grip depend on pressure or width, and neither does the lean formula. Pressure is therefore a refinement on top of the surface, which is why it deserves attention mostly when the road is wet, cold or rough.
Typical pressures for 25–32 mm
Schwalbe publishes pressures by width and rider weight for its Pro One TLE on a 19 mm inner-width rim. Rear pressure is slightly higher than front because the rear wheel carries more.3
| Width | Rider 55–59 kg | Rider 81–85 kg |
|---|---|---|
| 25 mm | 4.8 / 5.0 bar (70 / 73 psi) | 6.8 / 7.0 bar (99 / 102 psi) |
| 28 mm | 4.0 / 4.2 bar (58 / 61 psi) | 5.8 / 6.0 bar (84 / 87 psi) |
| 30 mm | 3.6 / 3.8 bar (52 / 55 psi) | 4.8 / 5.0 bar (70 / 73 psi) |
| 32 mm | not in that table | The tester ran 4.5 bar (65 psi) on its 32 mm tyre |
Read it as a starting point for one tyre. Your tyre model, rim width, tubeless or not, and weight shift the answer, and the maximum printed on the tyre and rim is a hard ceiling. In that table the wider tyres run roughly 0.4–1.0 bar lower at the same rider weight, and a heavier rider needs more. Use the manufacturer’s chart or calculator for your own tyre and check the number a few rides in.
Why pressure that is too high gives less grip on poor asphalt
Surface impedance is the energy lost when bumps push the tyre, bike and rider up and down. A low-pressure tyre absorbs more of that, and the rougher the road, the lower the pressure at which a tyre performs best.4 The same source gives an example on new asphalt: 10 psi below its calculated sweet spot cost very little speed, while 10 psi above cost many times more. It also notes that when grip matters most, such as in mud, the right pressure is lower still. That is a speed calculation, not a grip test, but it shows the shape: too low is forgiving, too high is not.
Grip follows from that by a standard argument rather than a measurement here. On a hard tyre the wheel is lifted and dropped by small bumps, so the load on the contact patch rises and falls. The tyre can only use the grip of the moment, and rubber gives less friction per newton as load increases, so the average is lower than at constant load. Add a patch that is small to begin with (see the table above) and a tyre that bridges the texture instead of settling into it, and a leaned-over wheel has less to give on patched, cracked or gritty asphalt. A tyre at a sensible lower pressure stays in contact more of the time. None of these effects is in Krengo’s model, which uses one assumed μ per surface.
What helps in practice
- Pick pressure from your tyre’s chart. Start at the chart value for your weight and width, then change by 0.2–0.3 bar at a time and notice how the bike feels in a corner you know.
- Go a little lower for wet and rough days. The rig data and the rough-road argument both point that way. Stay above the level where the tyre squirms or the rim can touch the road.
- Use the widest tyre your frame takes. Wider gave more wet grip in the same tester’s comparison, and it lets you run lower pressure.2
- Check pressure before the ride. Tubeless and latex tyres lose pressure overnight. A gauge beats a thumb.
- Keep the line and the speed work. A wider radius, braking while upright and smooth inputs are still the biggest gains. See road bike cornering technique and cornering in the rain.
Try your own corner in the lean angle calculator and see the colours in the grip scale. Krengo shows lean and an estimate of how much of the assumed grip the corner uses. It does not sense the tyres or the road, so never read green as permission to go faster.
Sources
- Bicycle Rolling Resistance, Wet grip tire pressure test. Continental Grand Prix 5000 S TR, Vittoria Corsa Pro TLR and Tufo Comtura Prima TR, all 28 mm, at 3.7, 5.0, 6.2 and 7.4 bar on a flat, textured ceramic plate. Used for the grip-by-pressure table. A rig result, not a road value. Read on 5 October 2026.
- Bicycle Rolling Resistance, Continental Grand Prix 5000 S TR 25, 28, 30, 32 mm comparison. Test pressures 5.5, 5.0, 4.8 and 4.5 bar; wet grip scores by width and the conclusion that bigger tyres give more grip. Read on 5 October 2026.
- Schwalbe, Road bike technology. Pressure table for the Pro One TLE on a 19 mm inner-width rim; tyre width may vary by ±1 mm with the rim. Read on 5 October 2026.
- SILCA, Tire pressure calculator explained. Surface impedance, the lower breakpoint pressure on rough surfaces, and the example of 10 psi below against above the sweet spot. It is a speed model. Read on 5 October 2026.
The contact-area relation A = F / p, the friction limit tan θ = μ, the lean formula and the argument about load variation are standard textbook models and are not taken from the sources. The lean angles and utilisation percentages are Krengo’s own model values with the grip scale’s assumed μ, level factor and margin. Applying the rig’s relative change to a wet road is an illustration.